Mesoscale Discussion – Severe storm potential over portions of the Chicago area

Weather
Mesoscale Discussion 0485
   NWS Storm Prediction Center Norman OK
   0333 PM CDT Tue Apr 28 2020

   Areas affected...eastern Missouri...southeast Iowa...into western
   Illinois

   Concerning...Severe potential...Watch likely 

   Valid 282033Z - 282200Z

   Probability of Watch Issuance...95 percent

   SUMMARY...Severe thunderstorms with the potential for damaging wind
   gusts and large hail with a tornado or two will be likely this
   afternoon and evening.

   DISCUSSION...Mid-level ascent from an approaching shortwave trough
   over the central High Plains is impinging on the warm sector of a
   surface cyclone over southern Minnesota and northern Iowa. Boundary
   layer moisture has increased through the day across Missouri and
   southern Illinois with surface dewpoints in the upper 50s into the
   low 60s F. As a result of the moistening, 1000-2000 J/kg of MLCAPE
   has developed across the area. The instability is concurrent with
   effective bulk-shear of 30 to 40 kt. Severe storms including a mix
   of line segments and a few supercells are likely to develop over the
   next 1 to 2 hours along the surface trough/cold-front trailing the
   surface low. Initially, these storms will pose a risk for a tornado
   or two but will transition to a damaging winds and hail threat.

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